Their lines are long! We lined up at 6:10pm for the Dwarves and met them at 7:10pm. They didn't come out until about 6:50pm and were close to the front. For the Dwarves line you are only allowed one group photo, no individuals.
The line for the Princesses does get busy. At this point we don't know what will change with Fairytale Hall as Anna and Elsa are moving in from April 20th. Last year, there was Rapunzel, Flynn, Snow White and her Prince on one side of the hall. The other side had Cinderella, Prince Charming, Aurora and Prince Phillip. Rapunzel and Flynns lines get long and average wait times were one hour +. Rapunzel one night had a 2 hour wait.
I would recommend that you line up for the Dwarves before the party starts. The line roughly starts from 6pm (sometimes earlier) but if you get in line by 6pm or so, you will be toward the front. This way you will be done by 7:15pm or so and you can use the rest of the partys hours.
Line up for Rapunzel or Cinderella while the first parade is on. Meet the two princesses and their Princes. Watch HalloWishes from Fantasyland. As soon as the fireworks are finished, get in line for the other Princess Set you didn't meet. Then head to Liberty Square to watch the second Parade. The second parade is always the quietest.